It is known to produce a silanized, pyrogenically made silicic acid by treating the pyrogenically made silicic acid with dimethyldichorosilane (Publish, Examined German Patent Application DE-AS 11 63 784).
Pyrogenically made silicic acids are also known that carry chemically bound --SiC.sub.8 H.sub.17 groups, trimethylsilyl groups, or polydimethylsiloxane groups on their surface (Schriftenreihe Pigmente [Publication Series, "Pigments"] No. 11, page 15, Aug. 1991 Edition).
The subject of the invention is silanized, pyrogenically prepared silicic acids, which are characterized in that the pyrogenically prepared silicic acids are treated with a compound selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, where n=from 10 to 18 and R stands for an alkyl, such as methyl, ethyl, or the like.
A silicic acid prepared by high-temperature hydrolytic means from SiCl.sub.4 +H.sub.2 and O.sub.2 can be used as the pyrogenically prepared silicic acid.
In particular, a temperature-hydrolytically prepared silicic acid can be used that has the following physical-chemical specifications:
TABLE 1 __________________________________________________________________________ AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL 90 130 150 200 300 380 OX TT __________________________________________________________________________ 600 Behavior with respect to water hydrophilic Appearance loose white powder Surface area in accordance with 90 .+-. 15 130 .+-. 25 150 .+-. 15 200 .+-. 25 300 .+-. 30 380 .+-. 30 50 200 .+-. 50 BET.sup.1) m.sup.2 /g Mean size of the primary particles, in nm 20 16 14 12 7 7 40 40 Stamping density .sup.2) ca. 80 ca. 50 ca. 50 ca. 50 ca. 50 ca. 50 ca. ca. 60 Normal goods g/1 -- ca. 120 ca. 120 ca. 120 ca. 120 ca. 120 -- -- Compacted goods g/1 (Additive "V") Drying loss .sup.3) &lt;1.0 &lt;1.5 &lt;0.5 .sup.9) &lt;1.5 &lt;1.5 &lt;1.5 &lt;1.5 &lt;2.5 (2 hours at 1000.degree. C.) % Upon leaving manufacturing plant Annealing loss .sup.4) .sup.7) % &lt;1 &lt;1 &lt;1 &lt;1 &lt;2 &lt;2.5 &lt;1 &lt;2.5 (2 hours at 1000.degree. C.) pH value .sup.5)(in 4% aqueous dispersion) 3.6-4.5 3.6-4.3 3.6-4.3 3.6-4.3 3.6-4.3 3.6-4.3 3.6-4.8 3.6-4.5 SiO.sub.2 .sup.8) % &gt;99.8 &gt;99.8 &gt;99.8 &gt;99.8 &gt;99.8 &gt;99.8 &gt;99.8 &gt;99.8 A1.sub.2 O.sub.3 .sup.8) % &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.08 &lt;0.05 Fe.sub.2 O.sub.3 .sup.8) % &lt;0.003 &lt;0.003 &lt;0.003 &lt;0.003 &lt;0.003 &lt;0.003 &lt;0.01 &lt;0.003 TiO.sub.2 .sup.8) % &lt;0.03 &lt;0.03 &lt;0.03 &lt;0.03 &lt;0.03 &lt;0.03 &lt;0.03 &lt;0.03 HC1 .sup.8) .sup.9) % &lt;0.025 &lt;0.025 &lt;0.025 &lt;0.025 &lt;0.025 &lt;0.025 &lt;0.025 &lt;0.025 Screen residues .sup.6) % &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.05 &lt;0.2 &lt;0.05 (Per Mocker, 45 .mu.m) __________________________________________________________________________ .sup.1) in reliance on DIN 66131 .sup.2) in reliance on DIN ISO 787/XI, JIS K 5101/18 (unscreened) .sup.3) in reliance on DIN ISO 787/II ASTM D 280, JIS K 5101/23 .sup.4) in reliance on DIN 55 921, ASTM D 1208, JIS K 5101/21 .sup.5) in reliance on DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24 .sup.6) in DIN ISO 787/XVIII, JIS K 5101/20 .sup.7) referred to the 2 hours at 105.degree. C. of dried substance .sup.8) referred to the 2 hours at 1000.degree. C. of the annealed substance .sup.9) HC1content is a component of the annealing loss
Pyrogenic silicic acids of this kind are known. They are described in the following literature, among other sources:
Winnacker-Kuchler, Chemische Technologie [Chemical Technology], Vol. 3 (1983), 4th Ed., page 77, and PA1 Silane I: (CH.sub.3 O).sub.3 SiC.sub.16 H.sub.33 (hexadecyltrimethoxysilane) PA1 Silane II: (CH.sub.3 O).sub.3 SiC.sub.18 H.sub.37 (octadecyltrimethoxysilane)
Ullmanns Encyklopadie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], 4th Ed. (1982), Vol. 21, p. 462.
The pyrogenically prepared silicic acids are treated with a compound selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, where n=from 10 to 18 and R stands for an alkyl, such as methyl, ethyl, or the like.
In particular, the following compounds can be used:
The silicic acids according to the invention can be prepared in that the pyrogenically prepared silicic acids are placed in a mixer, and while being mixed intensively the silicic acids are sprayed, optionally first with water and then with the compound (organosilane) selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, mixing is continued for from 15 to 30 minutes, and then temperature stabilization is done at a temperature of from 100.degree. to 160.degree. C. over a period of time from 1 to 3 h.
The water used may be acidified with an acid, such as hydrochloric acid, to a pH value of from 7 to 1.
The organosilane used can be dissolved in a solvent, such as ethanol.
The temperature stabilization can be carried out in a protective gas atmosphere, for instance in nitrogen.
The pyrogenically prepared silicic acids, silanized with silane I, according to the invention have the physical-chemical specifications listed in Table 2:
TABLE 2 __________________________________________________________________________ E duct A 90 A 130 A 150 A 200 A 300 A 380 OX TT __________________________________________________________________________ 600 Mean size of the primary particles [nm] 20 16 14 12 7 7 40 40 Surface area per BET [m.sup.2 /g] 40-90 60-130 75-150 100-200 150-300 200-380 20-50 100-250 Stamp density [g/1] 40-140 40-140 40-140 40-140 40-140 40-140 40-140 40-140 Drying loss [%] &lt;2 &lt;2 &lt;2 &lt;2 &lt;2 &lt;2 &lt;2 &lt;2 Annealing loss [%] 0.1-10 0.1-10 0.1-10 0.5-15 0.5-20 0.5-25 0.1-10 0.5-20 Carbon Content [%] 0.1-10 0.1-10 0.1-10 0.5-15 0.5-20 0.5-25 0.1-10 0.5-20 pH Value 3.5-5.5 3.5-5.5 3.5-5.5 3.5-5.5 3.5-5.5 3.5-5.5 3.5-5.5 3.5-5.5 __________________________________________________________________________
The silicic acids according to the invention are not dispersed in a solvent and can be employed as thickening agents in liquids, such as water-dilutable paints, and resins such as epoxy resins. The silicic acids according to the invention can also be employed in silicon rubber, rubber, cosmetic articles, toner powders, and as agents for improving pourability and also as reinforcing fillers.